Although stopping brakes in robots are generally extremely reliable, the risk of failure should be reduced further, particularly for safety critical situations.
However, the problem arises, when using actuators with only one brake, of realizing the maximum acceptable residual risk of an unwanted movement by a single-channel system.
Carrying out a periodical brake test in order to record creeping changes in brake performance is therefore known in accordance with in-house practice. If preset performance criteria are not met, the respective brake is replaced. This method is, however, not appropriate for situations where braking performance decreases spontaneously.
Another method known from in-house practice therefore consists in not closing the brake or not using it at all, in particular in safety critical situations. The axis is actively brought to a standstill instead by means of a correspondingly controlled actuator torque thereby falling under stop category 2 according to DIN EN 60204-1:2007-06, which defines three categories of a stop function for manipulators:    Stop 0: uncontrolled stopping through immediate interruption of the power supply to the machine actuators;    Stop 1: controlled stopping where the power supply to the machine actuators is still available in order to achieve the stop. The power supply is removed when the stop is achieved or the reliable period for stopping has been exceeded; and    Stop 2: controlled stopping where the power supply to the machine actuators is left available.
In terms of control technology, these three categories can be implemented in different ways.
If the axis is actively brought to a standstill by a closed brake by means of a correspondingly controlled actuator torque, this results in the disadvantage of keeping the manipulator in an active state, which requires power, and can also result in noise pollution.